Greek Astronomers Watch Giant Star Transform in Real Time

The news in Greek

1. παρατηρώ
   Κοιτάζω κάτι με προσοχή για να μάθω περισσότερα γι’ αυτό. ↩︎
2. γαλαξίας  (m.)
   Ένα πολύ μεγάλο σύνολο από αστέρια, αέρια και σκόνη στο διάστημα. ↩︎
3. κίτρινος
   Έχει το χρώμα του ήλιου ή του λεμονιού. ↩︎
4. μελετώ
   Εξετάζω κάτι πολύ προσεκτικά για να το καταλάβω καλύτερα. ↩︎
5. δεδομένο  (n.)
   Πληροφορίες και αριθμοί που συλλέγονται για να μελετηθούν. ↩︎
6. καταλαβαίνω
   Αντιλαμβάνομαι τη σημασία ή την αιτία κάποιου πράγματος. ↩︎

Translation

Text comprehension

Question 1: Where is the star WOH G64 located?

Question 2: How many years of data did the scientists study to understand why the star changed?

Vocabulary

Greek	English
παρατηρώ	to observe
γαλαξίας  (m.)	galaxy
κίτρινος	yellow
μελετώ	to study
δεδομένο  (n.)	data
καταλαβαίνω	to understand

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Researchers at the National Observatory of Athens have observed a rare stellar transformation unfolding in real time, after noticing that one of the largest known stars in the universe appeared to have changed almost beyond recognition.

The star in question is WOH G64, located in the nearby galaxy known as the Large Magellanic Cloud. Since its discovery in the 1980s, it had been classified as one of the brightest, coolest, and largest red supergiants, with a radius 1,540 times greater than that of the Sun. When the Athens team examined it recently, however, they found it was no longer red and cool — it was yellow and more than 1,000 degrees Celsius warmer.

“At first we were completely lost with the measurements we were taking, so it was like a puzzle for which we had to find all the pieces,” said Dr Gonzalo Muñoz Sánchez, who led the study as part of his doctoral thesis at the National Observatory of Athens and the National and Kapodistrian University of Athens.

To piece together what had happened, the team analysed brightness measurements spanning more than 30 years, beginning in 1992, and combined them with new and archived electromagnetic spectra. Data came from sources including the Polish OGLE programme and the Las Campanas telescope in Chile.

“We were very lucky because for this particular galaxy we had a great deal of data from the last 30 years, so there was a treasure trove of archival material,” said Dr Alceste Bonanos, research director at the National Observatory of Athens and the study’s scientific lead.

According to the findings, published in the journal Nature Astronomy, the star dimmed in 2011, then brightened and became yellower and hotter between 2013 and 2014, before dimming significantly again in 2025. Its atmospheric chemical composition also changed.

The researchers also discovered for the first time that WOH G64 is part of a binary star system. Its companion is a star similar to the Sun but several times more massive, hotter, and brighter, emitting mainly blue light.

Two scenarios have been proposed to explain the changes. In the first, the binary system was surrounded by a large envelope that made it appear as a red supergiant; when that envelope dispersed, the two stars were revealed. In the second, WOH G64 was always a yellow supergiant, and an outburst of material that ended around 2014 had made it appear red and cooler for several decades.

Red supergiants are stars with a mass more than eight times that of the Sun and a relatively short lifespan of just one to ten million years, before they eventually explode as supernovae. The research was funded by the European Research Council.